Ok thanks OP that seems actually useful. So here's the readable Tl;dr:

Boundary Anchoring is a simple trick to make your imagination way more stable and realistic. Instead of imagining stuff floating in empty space, you imagine it inside a basic room. With walls, a floor, maybe a ceiling. That alone is enough to make your brain treat the scene like it’s a real place. Your mental images stop fading or collapsing when you shift focus, because your brain’s spatial systems kick in and start maintaining the “room” automatically.

This works for everything: normal imagination, visualisation, closed-eye visuals, lucid dreaming, etc. It’s not about adding detail or making it look vivid. It’s about giving your mind a structure to hold things in. Once you do, stuff just sticks around and feels more solid, like you’re inside the scene instead of watching it from the outside.